In the related art, it has been known a radiation detector including: a scintillator including a first end surface and a second end surface opposite to in a predetermined direction; a first photodetector that detects light emitted from the first end surface of the scintillator; a second photodetector that detects light emitted from the second surface of the scintillator; and a position specifying unit that specifies a radiation incident position on which a radiation has been incident in the scintillator, based on each result detected by the first and second photodetectors (for example, referred to WO 2012/105292 and WO 2012/093526).